A substrate controlled, very highly diastereoselective Morita–Baylis–Hillman reaction: a remote activation of the diastereofacial selectivity in the synthesis of C-3-branched deoxysugars

The Morita–Baylis–Hillman (MBH) reaction of p-nitrobenzaldehyde with C (6) acyl protected enuloside in the presence of TiCl4/TBAI yielded highly diastereoenriched C-3-branched deoxysugar derivative or MBH adduct in high yield, while reactions of unprotected enuloside and C (6) alkyl protected enulosides with p-nitrobenzaldehyde under the same conditions afforded the adducts and , respectively, in low yield with moderate selectivity. Several representative aromatic and aliphatic aldehydes were selected to undergo MBH reaction with to give their respective adducts in very good yield with a very high diastereoselectivity. A plausible mechanism based on the assumption of a Zimmerman–Traxler-type transition state was proposed to explain the excellent selectivity observed with adducts derived from . The synthetic application of these adducts were shown by their stereoselective reduction to corresponding threo isomers in very good yield.